In general, a step of forming a thin film on a surface of a semiconductor wafer, an LCD substrate or the like and a step of etching the thin film into a desired pattern are repeatedly performed, in order to form an integrated circuit such as an IC or the like, or a logic element.
In a film formation step performed by a film formation device, a specified process gas (source gas) is caused to react within a processing vessel, whereby a thin film of silicon, a thin film of silicon oxide or silicon nitride, a thin film of metal, or a thin film of metal oxide or metal nitride is formed on a surface of a workpiece. An extra reaction byproduct is generated simultaneously with a film formation reaction. The extra reaction byproduct or an unreacted process gas is discharged together with an exhaust gas.
The reaction byproducts contained in the exhaust gas or the unreacted process gas, if directly discharged to the atmosphere, may cause environmental pollution, etc. In order to prevent this situation, it is typical to install a trap mechanism interposed in-between an exhaust system extending from a processing vessel. Thus, the reaction byproduct contained in the exhaust gas or the unreacted process gas is collected and removed.
Depending on the characteristics of the reaction byproduct or the like to be collected and removed, the trap mechanisms of various configurations are proposed. In case of removing a reaction byproduct condensed (liquefied) or coagulated (solidified) at a normal temperature, a trap mechanism is configured by, e.g., a plurality of fins installed within a housing having an exhaust gas inlet and an exhaust gas outlet. The fins are sequentially disposed along a flow direction of an exhaust gas. When the exhaust gas passes through between the fins, the reaction byproduct or the like within the exhaust gas is attached to the surface of the fins and thereby collected. In order to increase collection efficiency, the fins are sometimes cooled by a coolant (see, e.g., Japanese Patent Laid-open Publication Nos. 08-083773 and 08-172083). There is also known a trap mechanism in which an exhaust gas is cooled by allowing the same to flow through a spiral pipe of a first trap and a liquid-phase reaction byproduct is collected by a second trap provided with cooling fins (see, e.g., Japanese Patent Laid-open Publication No. 2001-297988).
In recent years, with a view to reducing a wiring resistance or a contact resistance, a thin film which contains a precious metal such as silver, gold, ruthenium or the like is formed by a film formation device using a raw material (source gas), such as an organic metal compound or the like containing the precious metal. In this case, a byproduct including an unreacted raw material is recovered by cooling and condensing an exhaust gas. Then, the unreacted raw material is recovered by purifying the byproduct (see, e.g., Japanese Patent Laid-open Publication No. 2001-342566).
The above-mentioned trap mechanisms have a difficulty in efficiently cooling a gas of a material, which is low in vapor pressure and thereby relatively hard to be liquefied, up to a temperature at which the gas can be collected. Thus, the trap mechanisms suffer low collection efficiency.